Known in the art is a random vibrations testing device comprising a noise generator, the output whereof is connected to paralleled narrow-band signal shaping channels, each of them incorporating a narrow-band amplification filter, the output whereof is connected to an input of a phase inverter paralleled with a switch, the output whereof is in its turn connected to an adder used commonly by all the shaping channels (cf. "Random Vibrations Spectrum Forming Systems" (in Russian) by Bozhko A.Ye. and Uretskiy Ya.S. Kiev, Naukova Dumka Publishing House, 1979, p. 62, FIG. 17).
Since a single adder is used in said device, the class of random vibration spectra being formed is narrow, the number of amplification narrow-band filters is large, and deep high-quality dips cannot be produced in the shaped signal spectrum.
There is also known a device proposed for testing articles acted upon by random vibrations, comprising a noise generator, the output whereof is connected to an input of a wide-band filter wherein an output is connected directly and through paralleled narrow-band in-phase signal shaping channels, each comprising a first pair of contacts of a switch, a narrow-band amplification filter, an attenuator and a second pair of contacts of the switch, to a means serving to form spikes and dips in the shaped signal spectrum and electrically coupled with opposite-phase narrow-band signal channels, each of them incorporating series-connected components including a pair of contacts of the same switch, the same narrow-band amplification filter, the same attenuator, a phase inverter, and a fourth pair of contacts of the same switch (cf. USSR Inventor's Certificate No. 393,631, class G01M 7/00).
An output of the switch in the foregoing device is connected to a power amplifier.
The means for formation of spikes and dips in the shaped signal spectrum of the device according to the invention is designed in the form of a single adder incorporating several inputs. Since the device is equipped with a wide-band filter connected to an input of the means for forming spikes and dips in the shaped signal spectrum, and is provided with narrow-band switching amplification filters, the number of narrow-band amplification filters can be reduced, and a more irregular random signal spectrum can be produced due to opposite-phase addition of the signals by the adder incorporated in the means for forming spikes and dips in the shaped signal spectrum.
Since several dips and spikes must be formed in the shaped signal spectrum, the device according to the invention is to be equipped with several narrow-band amplification filters connected directly or through phase inverters to the adder of the means for forming spikes and dips in the shaped signal spectrum.
The above method of connection of the narrow-band amplification filters does not provide for ideal amplitude response characteristics, and does not therefore permit producing deep dips in the shaped signal spectrum reaching zero level on frequencies corresponding to the center frequencies of said amplification filters.